1. Field of the Invention
This invention relates to an improved heat exchanger-incorporated hollow fiber type artificial lung
2. Description of the Prior Art
Generally, when blood is drawn out of a patient's body and oxygenated externally as during a cardiac operation, an artificial lung is used in the extracorporeal circut. When the cardiac operation necessitates use of slighly or medially low temperatures or extremely low temperatures, the blood must be cooled to the order of 35.degree. to 20.degree. C. at the outset of the circulation of blood through the extracorporeal circuit. Conversely when the extracorporeal circulation is to be terminated, the blood must be heated to a temperature substantially equal to the patient's body temperature. For the purpose of this regulation of blood temperature, the extracorporeal circuit is provided with a heat exchanger. This heat exchanger may be utilized for the purpose of maintaining the warmth of blood when the blood is desired to be circulated at the normal body temperature.
Conventionally in the extracorporeal circuit, the artificial lung and the heat exchanger have been incorporated independently of each other and interconnected with a connection tube. As a consequence of this setup, the assemblage of the circuit has proved complicated and the connection between the artificial lung and the heat exchanger has sometimes been made incorrectly, though not frequently. Moreover, since the connection tube is inevitably provided with two independent blood ports (one for the heat exchanger and the other for the artificial lung), it has called for a large volume of priming. Further, the operation of priming itself has been quite difficult because the removal of bubbles from the blood during the course of priming must be performed separately for the artificial lung and the heat exchanger.
As a partial solution of this problem, a superposed membrane type artificial lung incorporating a heat exchanger has been disclosed in Japanese Patent Publication (Kokoku) No. 2982/1980. Since the artificial lung part and the heat exchanger part are both of a superposed membrane type, the artificial lung is difficult to manufacture. Moreover, the artificial lung of such a membrane type admits a heavy personal error and has a possibility of entailing dispersion of quality among artificial lungs manufactured at one and the same factory.
To solve the problem, a heat exchanger-incorporated hollow fiber type artificial lung has been proposed. The lung includes a hollow fiber type artificial lung part having a plurality of bundles of gas-exchange hollow fiber membranes contained in a first tubular housing, and a shell-and-tube type heat exchanger part having a plurality of tubes contained in a second tubular housing, with the aforementioned artificial lung part and the aforementioned heat exchanger part coaxially connected to each other through the union of the first and second tubular housings (Japanese Patent Application No. 115,868/1980). In this artificial lung, the first and second housing have connecting ends of an identical diameter. These connecting ends have screw threads cut in manually opposite directions. The first and second housings are connected to each other through the medium of an O-ring by virtue of a connecting screw ring fitted across the outer sides of the aforementioned connecting ends.
The artificial lung adopting such mode of connection as described above is effective for a short period of time. When this artificial lung as a product is required to guarantee good performance for a long time, it may possibly pose some problems. If the screw threads in the connecting ends should come loose, since one of them spirals opposite the other, the user could not easily retighten them. When he dares to retighten such loose screw threads, thre is a possibility that he will unwittingly cause them to separate from each other entirely. In the hope of precluding such problem the feasibility of a method of fusing the reverse screw ring fast in position has been studied, only to find that the potting member of the artificial lung would collapse on prolonged exposure to compression, and the O-ring made of rubber would avoid following the collapse and induce leakage. When the O-ring separates from the groove formed exclusively for its insertion, it will induce leakage afterward.
An object of this invention is to provide a heat exchanger-incorporated hollow fiber type artificial lung provided with a highly relieable, safe connection structure.